Test Strategies: Automated Optical Inspection & Functional Test
Visit SiteDeciding the best test strategy for your printed circuit board assembly (PCBA) product can be both a daunting and challenging task. Does Automated Optical Inspection (AOI) catch every manufacturing defect? Is a customized In-Circuit Test (ICT), or a flexible Flying Probe Test (FPT) better suited for your specific product? Should you utilize an automated functional test (FCT) solution in order to fully test how your product will perform in-field? Or, is it a combination of one or more?
Since every test option has both strengths and weaknesses, it’s important to discuss your options with your electronic contract manufacturer by closely analyzing each test solution.
Last week, we looked at In-Circuit Test and Flying Probe Test in detail by comparing and contrasting these two test solutions. This week, we’re going to delve into the options, and various nuances, available with Automated Optical Inspection (AOI) and Functional Testing (FCT). While these two solutions have very different test strategies, they both offer excellent test coverage for a variety of printed circuit board assembly (PCBA) types.
AOI performs a visual inspection of SMT placements on any PCBA, and suits both high and low volume products. AOI has become pervasive in recent years, and is the standard practice for most, if not all, EMS providers. At Saline Lectronics, we utilize Mirtec systems to perform 100% AOI on all SMT placements.
AOI quickly inspects the PCBA for any solder quality concerns, polarity issues, part markings, and missing components. Since this solution is so fast (a PCBA is reviewed in a matter of seconds) and individual tooling per assembly is not required, we’ve made it a standard process for all of our SMT components. Due to the low cost and ease of implementation, AOI is the preferred solution for many clients. The speed of inspection also allows in-line processing, providing immediate feedback to upstream processes to make adjustments in real-time to prevent future defects during the production run.
What is unique about AOI is that it gets more intelligent every time it inspects an assembly. Since an Operator audits the AOI process, and reviews any errors that the machine alerts during a production run, the information that the Operator feeds back into the program helps to improve the AOI software, telling the machine which alerts are false. This teaches the program to be more intuitive for each subsequent production run.
Automated Optical Inspection Strengths:
- Fast test speed
- No tooling required
- Finds missing components
- Verifies solder quality
- Feeds information back into the process
- Verifies polarity orientation
Automated Optical Inspection Weaknesses:
- Inspects SMT components only
- No electrical testing
- Checks against data from the gerber files
- Does not check value of unmarked components
While AOI is a good solution for visual inspection, it does have its limitations and should be coupled with another type of testing solution. Since we offer 100% AOI inspection as standard on all of the assemblies that we manufacture, we highly encourage our customers to implement another testing solution to truly vet the performance of their products.
FCT is best suited for products with a complex design that need to simulate system performance or require tuning/adjustments to be made during test. As an end-use testing solution, FCT is better suited for products with a stable design that are no longer in the prototyping phase. Every single FCT solution is different, and will be completely dependent on the product type and what specifically needs to be tested. Many of our customers use FCT as an opportunity to simulate what the PCBA will actually be doing in-field to verify that all components are working together and performing as designed.
FCT can be a higher cost solution, both up-front and per unit costs, depending on the complexity of the test bed and the type of test that needs to be performed. We perform a variety of functional tests and test time can range from 1 minute to 15 minutes, subject to the quantity and length of tests performed. Due to this customization, lead time and tooling can take longer than other test solutions.
Functional Testing strengths:
- Assembly test solution – tests components working together
- Powers board and checks functionality
- Tests fit and functions of interconnecting devices
- Provides good test coverage
Functional Testing Weaknesses:
- Longest test time (depending on complexity)
- Custom tooling required
- Programming required
- Does not test tolerance of components
If you’re still unsure as to which testing strategy to implement, review the infographic below to help get a visual perspective on the similarities and differences between the test options that we’ve discussed.
In an ideal world, a PCBA should have multiple test solutions integrated into the final design. With a stable and mature product, we recommend that our clients utilize AOI (which is standard), FCT to simulate end-use performance, and either ICT or FPT depending on the product’s monthly volumes.
What we’ve reviewed in these two blog posts only highlights part of the testing solutions that we offer at Saline Lectronics. We perform many variations of the testing discussed as well as extended temperature and vibration testing capabilities. Ultimately, we recommend being involved up-front during the product design phase to assure that any design for test hooks are built into the product. Our goal is to help our customers with the best test strategy to ensure that the product functions as designed, directly out of the box.